1. Field of the Invention
This invention relates to digital image processing. More specifically, the invention is a method for optimizing the visual quality of any digital image based on contrast, lightness and sharpness measures thereof.
2. Description of the Related Art
The image of a scene captured by imaging equipment is affected by the environments between the imaging equipment and the scene. For example, if the environment is a low-light environment, image features can be lost due to flow contrast and low lightness. If the environment is turbid (e.g., foggy, smoke, rain, snow, murky water, etc.), there is very little contrast in an image. The combination or low light and a turbid environment makes image feature detection even more difficult.
Conventional image processing approaches are typically designed to cope with one of these environments but not the effects caused by combinations of these environments. Further, conventional image processing approaches are either manual methods or passive automatic image enhancement methods that do not evaluate and adapt to visual qualities. The manual methods require significant operator training, are time consuming and expensive, and/or are inconvenient for some applications. Existing automatic methods include auto level enhancement, histogram enhancement, and retinex image processing as disclosed in U.S. Pat. Nos. 5,991,456, 6,834,125 and 6,842,543.
Auto level or “fixed gain” enhancement does not work with wide dynamic range images as saturation occurs. Histogram enhancement performance is unpredictable. Retinex image processing performs relatively well in terms of contrast and lightness enhancement across wide ranging imaging conditions. However, the effectiveness of retinex image processing is reduced for narrow dynamic range images generated in low-light or turbid environments. Finally, each of the automatic enhancement approaches operates on all images even when some images are visually acceptable. From a processing cost perspective, this is inefficient.